To keep pace with the increasing density of active devices in ICs (integrated circuits), development of new isolation schems plays a critically important role in fabricating relatively modernized ICs. A promising alternative among the new isolation schemes is a trench isolation structure and the process for making it.
However, a conventional or prior-art trench isolation structure in ICs usually suffers problems such as current leakage at the corners of a trench, resulting in significant device current leakage in ICs, especially when there's any recess in the trench isolation structure. Consequently various raised trench isolation structures have been suggested as keys to the problem, among which one is the art disclosed in U.S. Pat. No. 5,733,383 and characterized by having a self-aligned cap or dome that is above the upper surface of the semiconductor substrate of an IC device and is formed through several processing steps to first construct a raised trench isolation structure 4 as shown in FIG. 1, and then to deposit insulating material 5 as shown in FIG. 2 conforming to the profile of the raised trench isolation structure 4 shown in FIG. 2. The insulating material 5 according to the prior art is thereafter processed by a step of dry etching to form spacers 6 as shown in FIG. 3, which are then preferably processed by a step of wet pad oxide etching to form a structure having a cap or dome as shown in FIG. 4.
It can be seen that the art suggested by U.S. Pat. No. 5,733,383 requires insulating material 5 to be deposited conforming to the profile of the structure and then etched in a critically sophisticated way in order to form the trench isolation structure shown in FIG. 4. The process for forming such a structure may rely too much on experience or even good luck, leaving a need of developing an alternative scheme for isolating ICs on the basis of trench structure, leading to the development of the present invention.